1. Field of the Invention
The present invention is generally related to the field of rotary travel limit stops and, more particularly, to an apparatus which provides the axial movement of a rotatable member following a preselected number of revolutions of that rotatable member from a predetermined initial position. After the rotatable member rotates the preselected number of revolutions, it is axially shifted to cause a first stop pin to engage a second stop pin, wherein the second stop pin is rigidly attached to a housing structure which supports the rotatable member.
2. Description of Related Art
Many different types of actuators have been used to move devices such as aircraft control surfaces. When those actuation devices reach end of travel positions, some means must be provided to cause the actuation system to stop. U.S. Pat. No. 2,852,630 which issued to Burrows on Sept. 16, 1958, discloses a limit switch actuator which provides a means for actuating limit switches on electrically operated cranes. The limit switches are used to shut off the drive to a drum or barrel when a rope or chain is fully wound thereon. The operating means of the actuator includes a shaft which carries two gear wheels having different numbers of teeth. One of the gear wheels is fixed on the shaft and the other gear wheel is loose. Both gear wheels mesh with a single pinion which is rotatable in a housing driven by the drum or barrel. The shaft is normally stationery so that the loose gear wheel is rotated thereon as the housing revolves and the gearwheels have parts which engage with one another after a given number of revolutions of the housing. Since the pinion is in mesh with two locked gear wheels of slightly different pitch, it also becomes locked on its axis because of the fact that the gear wheels have numbers of teeth which differ from each other and have a dog or stop on the side which faces the other wheel. This enables one of the wheels to lock with the other wheel when the dogs come into contact with each other.
U.S. Pat. No. 3,147,629 which issued to Michalec on Sept. 8, 1964, discloses a multiturn stop mechanism. This multiturn stop mechanism comprises first and second gears mounted for independent rotation about a common axis and axially spaced a short distance. These gears are mechanically interconnected by auxiliary gearing with the various ratios being selected so that the first and second gears rotate at different rates. The second gear may have one more tooth than the first while the auxiliary gearing may be a single pinion meshing with both gears. Each gear has a small protuberance or block fastened to that side which adjacent to the other gear and the blocks are positioned at substantially equal radial distances from the common axis. A multilobed locking device such as a multifigured arm or star wheel is pivoted about an axis parallel for the common axis and is so placed that one lobe always extends between the gears into the path of movement of the blocks. Each revolution of the gears brings the blocks closer together by one gear tooth space until a point is reached at which engagement of one lobe by the first block causes the next lobe to abut the second block, thereby providing a positive stop.
U.S. Pat. No. 3,203,262 which issued to Beer on Aug. 31, 1965, discloses a limited multiple turn rotary mechanism. The mechanism comprises two gears of substantially equal diameter mounted for independent rotation about a common axis and axially spaced a distance on the order of the thickness of the gears. The number of teeth in the two gears differ by one and both are driven by a common pinion gear. Thus, the gears rotate at different rates. Near the periphery of each gear on the facing sides a small block is fastened which extends toward but does not touch the other gear. A multilobe cam wheel is mounted for rotation so that the cam lobes extend between the gears and into the path of the blocks. As the gears rotate, the blocks approach each other until a point is reached at which one block engages one cam lobe and the other block another cam lobe which prevents further movement.
U.S. Pat. No. 3,662,610 which issued to Thoen on May 16, 1972, discloses a multiturn limit stop apparatus. The mechanism comprises a pinion, a gear in engagement with the pinion and stop members affixed to the pinion and gear. The ratio of the number of gear teeth to the number of pinion teeth is not an integer. The stop member affixed to the pinion extends beyond the periphery of the pinion and sweeps out an epitrochoidal path with respect to the gear pitch circle as it rotates. The stop member affixed to the gear is positioned inside the gear pitch circle. Since the ratio is not an integer, the epitrochoidal loops of the pinion stop member rotate with respect to the gear pitch circle on each gear revolution. Rotation in one direction is limited when the epitrochoidal path for the pinion stop member on a particular rotation contacts the gear stop member.
U.S. Pat. No. 4,064,981 which issued to House et al on Dec. 27, 1977 discloses a limit stop apparatus. The apparatus comprises a driven shaft which rotates a predetermined number of revolutions in either direction whereupon a traveling nut assembly contacts a shock absorbing stop to terminate shaft rotation by frictionally jamming screw threads between the nut assembly and the driven shaft. Outer and inner portions of the nut assembly are connected for limited relative rotational motion on nonjamming auxiliary threads, thus permitting the driven shaft to backed off to release the nut assembly from the shock absorbing stop and thereby release the jammed threads with a minimum of available torque. By this structure, locking of the limit stop at either end is prevented.
U.S. Pat. No. 4,641,737 which issued to Gillingham et al on Feb. 10, 1987, discloses a bi-directional overtravel stop. The overtravel stop has a pair of gears associated with the shaft to rotate their width. Each gear engages an associated limiting gear and the two engaged gear pairs have different gear ratios. One of the limiting gears is threaded over a shaft which is secured for rotation with the other limiting gear, such that the different gear gear ratios causes the one limiting gear to translate over the shaft. At selected travel limits, the one limiting gear is caused to lock relative to the other, thereby, causing one of the gears associated with the shaft to shift their around. A cam structure is provided whiCh axially shifts a stop member associated with the shaft into engagement with a fixed stop when the one gear shifts about the shaft. Two different cam structures are shown including a pin and slot connection between the stop member and the shaft and an ear and cam recess connection between the stop member and one of the shaft gears.
Co-pending patent application (S.N. B360509), which is assigned to the assignee of the present application, discloses a rotary travel limit stop mechanism which comprises a first gear that is disposed in gear mesh association with second and third gears. The second and third gears are provided with different numbers of teeth so that they rotate at different rates when the first rotatable member rotates. The different rates of rotation cause the second and third gears to rotate relative to each other. The third gear is provided with an annular groove which has a varying depth. The second gear is provided with a pin which is slidably associated in a hole of the second gear. The annular groove of the third gear is associated with the head of the pin and, when the second and third gears reach a preselected position relative to each other, the head of the slidable Pin is caused to move axially with respect to the second gear due to the decreased depth of the groove in the third gear. This movement causes a portion of the pin to move into interfering relation with a fixed stop pin and, when the slidable pin contacts the fixed stop pin, further rotation of the gear members is prevented.